Bolivian President Evo Morales led in early returns from the first round of Sunday’s presidential election, but seems not to have enough votes to avoid a runoff.

The country’s electoral authority said a preliminary count of 84 per cent of the votes showed Mr Morales on top with 45.3 per cent, followed by 38.2 per cent for his closest rival, former President Carlos Mesa.

If the results hold, the two men will face off in December and Mr Morales could be vulnerable to a united opposition in the first runoff in his 14 years in power.

Mr Mesa told supporters shortly after the first results were announced that his coalition had scored “an unquestionable triumph,” and he urged others parties to join him for a “definitive triumph” in the second round.

In a surprise result, Chi Hyun Chung, a physician and evangelical pastor of South Korean ancestry, was in third with 8.8 per cent of the vote

To avoid a runoff and win outright, Mr Morales would have needed to get 50% of the votes plus one or have 40 per cent and finish 10 percentage points ahead of the nearest challenger.

Mr Morales came to prominence leading social protests in the landlocked country of 11 million people and rose to power as Bolivia’s first indigenous president in 2006. The 59-year-old leftist is South America’s longest-serving leader.

Mr Mesa is a 66-year-old historian who as vice president rose to Bolivia’s top office when his predecessor resigned the presidency in 2003 amid widespread protests.

He then stepped aside himself in 2005 amid renewed demonstrations led by Mr Morales, who was then leader of the coca growers union.

Voting, which was mandatory, was mostly calm, though police said they arrested more than 100 people for violating the country’s rigid election-day rules against drinking, large gatherings or casual driving.

In a surprise result, Chi Hyun Chung, a physician and evangelical pastor of South Korean ancestry, was in third with 8.8 per cent of the vote.

It's not against Evo, it's against me, against the poor people, against the humble

Celestino Aguirre

Mr Morales voted early in the coca-growing region of El Chapare, where residents threw flower petals at him and he said he remained confident of his chances.

In his years in office, he allied himself with a leftist bloc of Latin American leaders and used revenues from the country’s natural gas and minerals to redistribute wealth among the masses and lift millions out of poverty in the region’s poorest country.

The economy has grown by an annual average of about 4.5 per cent, well above the regional average.

Mr Morales, the son of Aymara Indian shepherds, has also been credited for battling racial inequalities.

Many Bolivians, such as vendor Celestino Aguirre still identify with “Evo,” as he is widely known, saying people should not criticise him so much. “It’s not against Evo, it’s against me, against the poor people, against the humble.”

But the president also has faced growing dissatisfaction even among his indigenous supporters. Some are frustrated by corruption scandals linked to his administration – though not Mr Morales himself – and many by his refusal to accept a referendum on limiting presidential terms.

While Bolivians voted to maintain term limits in 2016, the country’s top court, which is seen by critics as friendly to the president, ruled that limits would violate Mr Morales’s political rights as a citizen.

Bolivians were also electing all 166 congressional seats. Polls projected that no party would have a majority in Congress, which could lead to an impasse for the upcoming administration.